Orthodontic treatments involve repositioning misaligned teeth and improving bite configurations for improved cosmetic appearance and dental function. Repositioning teeth is accomplished by applying controlled forces to the teeth over an extended period of time. This is conventionally accomplished by wearing what are commonly referred to as “braces.” Braces include a variety of appliances such as brackets, bands, archwires, ligatures, and O-rings. After braces are bonded to the teeth, periodic meetings with an orthodontist are typically required to adjust the braces. This may involve installing different archwires with different force-inducing properties and/or may include replacing or tightening existing ligatures. Between meetings, the patient may be required to wear supplementary appliances, such as elastic bands or headgear, to supply additional or extraoral forces.
Although conventional braces can be effective, their use often is a tedious and time consuming process that requires many visits to an orthodontist. Moreover, from a patient's perspective, braces are unsightly and uncomfortable. Consequently, alternative orthodontic treatments have developed. A particularly promising approach relies on the use of elastic positioning appliances for realigning teeth. Such appliances comprise a thin shell of elastic material that generally conforms to a patient's teeth, but that is slightly out of alignment with the patient's initial tooth configuration. Placement of the elastic positioner over the teeth applies controlled forces in specific locations to gradually move the teeth into the new configuration. Repetition of this process with successive appliances having different configurations eventually moves a patient's teeth through a series of intermediate configurations to a final desired configuration. A full description of exemplary elastic polymeric positioning appliances and methods of using same are described in U.S. Pat. No. 5,975,893, commonly assigned to the assignee of the instant invention and which is incorporated herein by reference in its entirety.
Polymeric positioning appliances, such as those described in the '893 patent, are advantageous over conventional braces in that they are easy to use and they are generally transparent, providing an improved cosmetic appearance. Unfortunately, polymeric materials currently utilized in the production of these positioning appliances may undergo stress relaxation and creep, which can seriously degrade the ability of an appliance to reposition teeth as desired. In addition, polymeric materials currently utilized may be susceptible to degradation as a result of exposure to saliva and other chemicals present within a patient's mouth.